Rate and Mechanism of the Oxidative Addition of Benzoic Anhydride to Palladium(0) Complexes in DMF

The rate constant of the oxidative addition of the benzoic anhydride (PhCO)2O to [Pd0(PPh3)4] has been determined in DMF and compared to that of phenyl halides and phenyl triflate. The following reactivity order has been established: PhI >> (PhCO)2O > PhOTf > PhBr. The oxidative addition of (PhCO)2O proceeds by activation of one C−O bond. Two acyl-PdII complexes are formed: a neutral complex trans-[(PhCO)Pd(OCOPh)(PPh3)2] and a cationic complex trans-[(PhCO)PdS(PPh3)2]+ (S = DMF) showing that the decarbonylation process is highly endergonic. The exchange of PPh3 by the bidentate ligand dppp does not favor the decarbonylation process.

Synthesis of Unsymmetrical Heterobiaryls Using palladium-catalyzed cross-coupling reactions of lithium organozincates

International audienceSeveral unsymmetrical heterobiaryls have been synthesized through palladium-catalyzed cross-coupling reactions of lithium triorganozincates. The latter have been prepared by deprotonative lithiation followed by transmetalation using non hygroscopic ZnCl2*TMEDA (1/3 equiv)

Études des phenomenes de transposition didactique de la statistique dans le champ universitaire et ses environnements : une contribution à la pédagogie universitaire

Statistics, with its particularity being a science based on analysis anddecision, generates interests from all scientific and social domains. Thus, statistics isa many-sided discipline based on shared dimensions, but also on specificformulations.Researchers must develop specific skills to explain each step of a statisticalapproach in both situations studied: doctoral theses and expertise. Additionally,results need to be communicated clearly and precisely by a researcher in order toassure their comprehension and the appropriation of knowledge. The analysis ofdoctoral theses highlights a regularity in the use of statistical concepts and statisticallanguage, but also numerous specificities for academic disciplines. Moreover, theanalysis of expertise highlights that researchers set up didactic approaches toimprove the transfer of knowledge to decision-making politics.This thesis aims to take part in the reflection about i) the teaching ofstatistics at the university and ii) the pedagogical strategies that needs to bedeveloped by highlighting the teaching strategies proven to be useful for statisticaleducation. Our analysis clearly shows the importance of qualifying students in thedissemination and communication of results from statistical analyses. Takentogether, there is a clear need to develop new teaching strategies for statistics at theuniversity aiming at developing teaching methods facilitating explicitcommunication of statistical expertise and results addressing a wide range ofaudiences.La spécificité de la statistique, en tant que science d’analyse et de décision,suscite l’intérêt de l’ensemble des domaines scientifiques et sociétaux. Elle endevient ainsi une discipline protéiforme s’appuyant sur des dimensions partagées,mais aussi sur des formulations spécifiques. Dans les deux situations étudiées,doctorat et expertise, le chercheur doit développer des capacités à expliciter lesétapes d’une démarche statistique et à communiquer de manière compréhensible àdes fins de diffusion et d’appropriation. L’analyse des thèses met en lumière desrégularités d’usage de concepts et de mots, mais aussi, de nombreuses spécificitésdisciplinaires. L’analyse de la situation d’expertise, quant à elle, souligne le travaildidactique mis en oeuvre par le chercheur afin de rendre possible le transfert deconnaissance à destination des politiques décisionnaires.Les différents éléments et analyses ayant constitué cette thèse ont pourobjet de participer à la réflexion sur l’enseignement de la statistique à l’université etsur les stratégies pédagogiques à développer. Notre analyse met en évidencel’importance de former les étudiants à la diffusion et la traduction de résultatsd’études statistiques. Tout ceci conduit à la question de la transformation desenseignements de la statistique à l’université afin de développer les temps et desméthodes d’apprentissage de diffusion, à visée d’explicitation, des savoirsstatistiques et des résultats auprès de publics variés

Nickel catalyzed one pot synthesis of biaryls under air at room temperature

A practical, room temperature catalytic system has been developed for the synthesis of biaryls in one step from the homocoupling of in situ generated Grignard reagents using the nickel(II) complex. Molecular oxygen used as an oxidant makes the system environment friendly. The reaction system is compatible with diverse functionality to afford biaryls in appreciable yields

A Convenient Approach to Luminescent Cyclometalated Platinum(II) Complexes with Organometallic π-Bonded Benzenedithiolate

International audienceA family of neutral cyclometalated platinum(II) complexes [(C^N)Pt(η-S^S)] with π-bonded benzenedithiolate {(η-S^S) = Cp*Ru(C6H4S2)} and various cyclometalated ligands, {(C^N) = 2-phenylpyridine (ppy), (2); 2,4-difluorophenylpyridine (F2ppy) (3), benzo[h]quinoline (bzq) (4); dibenzo[f,h]quinoline (dbzq) (5) } were prepared and fully characterized. For comparison purposes the related bipyridine platinum (II) complex [(bpy)Pt(η-S^S)][OTf] (6) was also prepared. The electrochemistry behavior of these complexes was investigated and shows the enhanced stability of these compounds toward oxidation due to the presence of Cp*Ru moiety which is now π-bonded to the benzenedithiolato group. Moreover several complexes were identified by single crystal X-ray molecular structures. To the best of our knowledge these are the first structures to be reported for cyclometalated platinum complexes with a π-bonded benzenedithiolate (bdt) ligand. All of the complexes are luminescent in fluid solution at room temperature and in glassy solution at 77 K; their emission properties can be tuned through ligand variation

Synthesis of di(Imdazolium) and di(Pyrazolium) Salts as Precursors for N-heterocyclic Dicarbene Complexes

Alpha,omega-bis(pyrazol-1-yl)alkanes and alpha,omega-bis(imidazol-1-yl)alkanes with spacers consisting of four to ten methylene groups have been prepared from pyrazole, 3,5-dimethylpyrazole or imidazole and corresponding dibromoalkanes in a superbasic medium KOH-DMSO. The proposed method of synthesis allowed the preparation of new flexible bidentate ligands without the need to use toxic solvents and tedious workup procedures. Bis(pyrazol-1-yl)alkanes were further functionalized for their use as precursors for “non-classical” mesoionic N-heterocyclic carbene ligands. One the first step, iodine atoms were introduced to positions 4 of pyrazole rings by oxidative iodination using I[2]-HIO[3] system. On the next step, nitrogen atoms in positions 2 of pyrazole rings were alkylated using several agents. Reaction with methyliodide unexpectedly led to the formation of only mono-alkylated products even after 7 days of refluxing in a neat alkyliodide. Methylation by trimethyloxonium tetrafluoroborate or methyltriflate led to dimethylated products in high yields. Bis(imidazol-1-yl)alkanes were easily alkylated by methyliodide to give di(imidazolium) salts – precursors to “classic” N-heterocyclic dicarbenes

Oxidative addition to palladium(0) Diphosphine complexes: Observations of mechanistic complexity with iodobenzene as reactant

Using a combination of electrochemical and NMR techniques, the oxidative addition of PhX to three closely related bis-diphosphine P2Pd 0 complexes, where the steric bulk of just one substituent was varied, has been analysed quantitatively. For the complex derived from MetBu2P, a rapid reaction ensued with PhI following an associative mechanism, and data was also obtained by cyclic voltammetry for PhOTs, PhBr and PhCl, revealing distinct relative reactivities from the related (PCx 3)2Pd complex (Cx=cyclohexyl) previously studied. The corresponding EttBu2P complex reacted more slowly with PhI and was studied by NMR spectroscopy. The reaction course indicated a mixture of pathways, with contribution from a component that was [PhI] independent. For the CxtBu2P complex, reaction was again monitored by NMR spectroscopy, and was even slower. At high PhI concentrations reaction was predominantly linear in [PhI], but at lower concentrations the [PhI] independent pathway was again observed, and an accelerating influence of the reaction product was observed over the concentration range. The NMR spectra of the EttBu2P and CxtBu2P complexes conducted in C6D6 shows some line broadening that was augmented on addition of PhI. NMR experiments carried out in parallel show that there is rapid ligand exchange between free phosphine and the Pd2Pd complex and also a slow ligand crossover between different P2Pd complexes. DFT calculations were carried out to further test the feasibility of C6D6 involvement in the oxidative addition process, and located Van der Waals complexes for association of the P2Pd0 complexes with either PhI or benzene. PhI or solvent-assisted pathways for ligand loss are both lower in energy than direct ligand dissociation. Taken all together, these results provide a consistent explanation for the surprising complexity of an apparently simple reaction step. The clear dividing line between reactions that give a di- or monophosphine palladium complex after oxidative addition clarifies the participation of the ligand in coupling catalysis. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Evolution of Teaching Strategies in a French ODL University Course

ISBN: 978-0-9805950-2-4International audienceThe university course on statistical methods in health at the Bordeaux School of Public Health, University of Bordeaux, has been run as an Open and Distance Learning (ODL) program since 2004 on the basics of statistical reasoning in the health field. The course is mainly for professionals. In more than ten years, about 1,000 people have been trained with over a third coming from sub-Saharan Africa. The program aims to meet a growing demand for statistical training from professionals from the south whose mobility is limited. Each year a satisfaction survey is sent to students with a view to improving the program. Even though participation in the survey is anonymous and not compulsory, it is a valuable source of comments and ideas. These have led to innovative pedagogical practices such as “tutored exercises” with individual correction, the use of new statistical software, summary sheets and flipped classrooms. However, benchmarking of the program has shown that more could be done. Teaching strategies should evolve within the framework of distance learning in terms of content, form and interactivity. This article discusses the development of these new educational strategies from their inception as well as future projects

Iron(II) catalyzed reductive radical cyclization reactions of bromoacetals in the presence of NaBH4: optimization studies and mechanistic insights

Abstract 5-Exo-trig radical reductive cyclization reactions of bromoacetals are catalyzed by iron in the presence of the reducing agent NaBH4. Both iron(II) and iron(III) were found to effectively mediate these reactions. As shown by cyclic voltammetry, iron(III) can be reduced to an iron(II) precatalyst before passing through an identical reaction mechanism in which monoelectronic activation of the substrate would occur by an anionic hydridoiron(I) complex. Further studies have established that both the substrate (iodo- vs bromo-derivative) and the precatalytic mixture are decisive in determining the reaction outcome

Elucidating dramatic ligand effects on SET processes: iron hydride versus Iron borohydride catalyzed reductive radical cyclization of unsaturated organic halides

An iron(II) borohydride complex ([(η1-H3BH)FeCl(NCCH3)4]) is employed as the precatalyst in iron-catalyzed radical cyclizations of unsaturated organic halides in the presence of NaBH4. Mechanistic investigations have established that the ligand bound to the metal center (acetonitrile versus ethylenebis(diphenylphosphine) (dppe)) plays a crucial role in the structure and reactivity of the active anionic iron(I) hydride ([HFeCl(dppe)2]−) and borohydride ([(η1-H3BH)FeCl(NCCH3)4]−) with unsaturated haloacetals. This work provides new insights into iron(I) hydride and borohydride species and their potential implication in single-electron processes